Radar scanner antenna feed



April 5 'r. MOSELEY 2,505,424

RADAR SCANNER ANTENNA FEED Filed Aug. 27, 19 46 2 Sheets-Sheet 1 INVENTOR. Zbm/fnsan I. Mase/g/ BY W 2mm ATTOINA-Yf April 25, 1950 T. l. MOSELEAY 2,505,424

RADAR SCANNER ANTENNA FEED Filed Aug. 27, 1946 2 Sheets- Sheet 2 INVHVTORI 75/77/1'050/7 Z Mose/ey BY Wi wam ATTOQVBJ Fig. 2 is an exploded view of the outer end 01 the antenna feed illustrated in Fig. 1.

Fig. 3 is a perspective view of a longitudinal section of the outer end of the antenna feed 3 includes a forwardly tapered hollow steel waveguide stem I of rectangular cross-section, the" long dimension of the section being in a vertical plane so that the radio frequency energy passing therethrough will vibrate in a vertical plane.

soldered or otherwise fastehed'to the base of the stem I is a circular base plate Zprovided with screw holes 3 by which it can be fastened to a suitable paraboloid reflector and to the wave-guide system forming a part of the scanner unit. As shown in Fig. 1, the base plate 2 is provided with a central rectangular opening 5 arranged to form a continuation of the rectangular stem conduit.

The opposed side walls 5 and 6 of the stem I extend forwardly beyond its top and bottom walls and are curled rearwardly and uniformly to form diametrically opposed window supports.

Soldered to and over the outer or forward ends of the top and bottom of the stem l is a steel die-stamped antenna cap 1 formed with rearwardly inclined side walls 8 and 9 and with a circular rim I I. Soldered over and to the rear face of the rim II and to the stem walls 5 and 6 is a pair of diametrically opposed and generally semicircular windows [2 and I3 made of low-loss Pyrex glass. However, prior to securing the windows l2 and I3 in place, the interior surfaces of the stem and its cap are silver-plated and palladium-flashed so as to make them good conductors.

In order to fasten and seal windows l2 and 13 to the cap 1 and the stem I so that they will withstand fifteen pounds of air pressure, it has been found desirable to go through the followingprocedure:

The outside edges of the window are painted with a Hanovia silver paste which deposits a thin layer of silver on to the edge. The entire window is then baked to a temperature of 600 C. and then cooled at a predetermined rate to 300 C after which it is removed from the oven and allowed to cool to room temperature. The baking procedure attaches the silver deposit firmly on to the glass edge so that it will not peel. After the windows have cooled to room temperature they are given a copper plate. The copper naturally only sticks to the silver coated edges. The copper plated edges are now tinned in preparation for soldering to the feedcap edge. The entire feed horn cap and assembly is now heated to a specific temperature and the windows placed thereon with their matching surfaces lined up. The specific temperature aforementioned is such that it keeps the tinned surface of the window molten. Upon the removal of the heating source the solder cools and forms a pressurized bond between the tinned window and its mating antenna cap surface.

A comparison of this method of attaching windows for pressurization purposes, to the standard practices used in the trade, indicates that the present method results in a feed horn having a longer life and one which is more consistently perfect, and forms a better pressurized joint.

Threaded to the cap 1 in alignment with the axis of the stem l is a short-tuning screw or button [4 by which the antenna feed is matched electrically to the wave-guide system or feeder transmission line with which it is designed to be associated. After the required matching has been effected by the tuning button, it is soldered to the feed cap in its adjusted position.

The antenna feed shown in Figs. 4 and 5 includes a forwardly tapered stem 2i, rectangular H in cross-section and twisted through an angle of 90. As in the case of the feed illustrated in Figs. 1, 2 and 3, the opposed side walls 22 and 23 of the stem are convergent so as to form a gradually tapered stem and the forward portions of these walls are reversely curved as at 24 and 25. S01- dered or otherwise secured to the forward edges 26 and 21 0f the top and bottom walls of the stem is a feed cap having anarcuate inner surface 29 substantially complementary to the curved surfaces of the side walls 22 and 23 and forming therewith a pair of diametrically opposed wave guides 3! and 32. Sealed to the outer ends of the walls 22 and 23 and to the peripheral rear edge of the cap 28 is a pair of semicircular lowloss Pyrex glass windows 33 and 34. The method of fastening and sealing these windows is the same as set forth with respect to the modification shown in Figs. 1, 2 and 3. Threaded through the cap 28 is an adjustable tuning button 35 by which the antenna feed can be matched with its associated wave-guide system or transmission line.

Secured to the base of the stem 2| is a circular base plate 36 by which the stem is secured to its reflector and connected with the wave-guide system of its associated scanner unit. j

From the above description it will be noted that I have provided an externallytunable antenna feed horn of very simple construction requiring for its manufacture only six parts, a base plate, a stem, a one-piece feed cap, a pair of glass windows, a tuning button, and a very effective method of sealing these windows in place. Due to the rearwardly directed wave guides formed by the curved ends of the stem, side walls and the interior surface of the feed cap, the radio frequency beam is reflected rearwardly to the reflector with a minimum formation of standing waves. Matching of an antenna feed of this type with its associated wave-guide system is effected by simply adjusting the tuning button and then soldering it in its adjusted position. In this connection, it is to be noted that the matching of this type of feed and the design of its cap depends upon the thickness of the windows. They should be of sufiicient thickness to increase .the distance between the tuning button and its closest contact point. Such a design further avoids the high power breakdown troubles now encountered in standard antennas.

x .Although dimensions of antenna feeds of this type are critical and must .be correlated to the radar scanner of which they form a part, the design herein disclosed is applicable to any antenna feed regardless of the specific dimensions required and which can only be determined by trial and error.

7 extending at one end beyond the top and bottom walls and being reversely curved, a cup-shaped cap stamped from an integral sheet of material and having a bottom, side walls diverging from the bottom and a circular rim, said bottom being formed with a central opening to receive a tuning button, a tuning button received within said opening, and a window formed of two curvilinear sections of glass having the same radius as said rim and adapted to seat behind said reversely curved portions of the side walls and adjacent 0 said rim, said glass sections being bonded to said stem and cap and serving to mount the cap on the stem.

TOMLINSON I. MOSELEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,129,712 Southworth Sept. 13, 1938 2,139,431 Vatter Dec. 6, 1938 2,415,103 Langstroth Feb. 4, 1947 2,422,184 Cutler June 17, 1947 2,423,073 Willoughby June 24, 1947 2,429,640 Mieher et a1 Oct. 28, 1947 2,430,568 Hershberger Nov. 11, 1947 

